A femtocell will hereinafter be described in brief.
Femto is a prefix in the metric system, denoting a factor of 10−15 or 0.000000000000001. Hence a femtocell or FBS refers to an ultra-small indoor Access Point (AP) for low-power home use or office use. Although the term “femtocell” is sometimes interchangeably used with “picocell”, the former is used in the sense of a more advanced cell. The femtocell is a small cellular base station (BS) connected to a broadband router and functions to connect 2nd Generation (2G) and 3rd Generation (3G) voice and data to a backbone network of a mobile communication service provider via the Digital Subscriber Line (DSL).
The above-mentioned femtocell has the following advantages.
Recently, a new research paper has proposed a method for the femtocell to expedite the spread of 3G technology and greatly increase indoor coverage. Up to 2012, it is expected that the number of the femtocell BS users throughout the world will increase to about one hundred and two million, and the number of access points (APs) serving as BSs will also increase to about thirty-two million. According to chief analyst of ABI Research, Stuart Carlaw, “From a technological standpoint, their better in-building coverage for technologies such as WCDMA, HSDPA and EVDO is an incredibly important aspect of service delivery. From a strategic and financial standpoint, the routing of traffic through the Internet Protocol (IP) network significantly enhances network quality and capacity, and reduces the OPEX that carriers expend on backhaul.”
Femtocells can expand cell coverage and increase the quality of voice service. Mobile communication service providers are expecting that subscribers may be familiar with 3G by providing data service via femtocells. The femtocells are also called femto base stations (FBSs) or femto Base Transceiver Stations (femto BTSs).
In summary, femtocells offer the following benefits 1) to 4).
1) Cell coverage improvement
2) Infrastructure cost decrease
3) New service offering
4) Fixed Mobile Convergence (FMC) acceleration.
One or more femtocells may be grouped on a service basis or geological area basis. For example, a femtocell group that can access only a specific MS may be referred to as a Closed Subscriber Group (CSG). A femtocell BS (FBS) recognizes a CSG ID of the MS so that it allows access of only the MS subscribed to the CSG.
FIG. 1 illustrates an exemplary network configuration including FBSs.
FBSs are new network entities added to a legacy network. Accordingly, the use of FBSs may bring about additions or modifications to an entire network structure. An FBS may directly access the Internet and function as a BS. Therefore, the FBS can perform almost all functions of a macro BS. In addition, the FBS may relay data from the macro BS to MSs.
In FIG. 1, the network is configured by adding a Femto Network Gateway (FNG) to the legacy network.
Referring to FIG. 1, the FNG may communicate with an Access Service Network (ASN) gateway and a Connectivity Service Network (CSN). The FNG may use an Rx interface for communicating with the ASN and an Ry interface for communicating with the CSN.
An FBS may access directly a Transmission Control Protocol/Internet Protocol (TCP/IP) Internet and receive a service from the CSN via the FNG. An MS connected to the FBS may receive services from the FNG or CSN in relation to IP Multimedia Subsystem (IMS) authentication, etc.
The FBS is connected to a BS or AP via an R1 interface. This means that the FBS may receive a downlink channel from a macro BS. The FBS may also transmit a control signal to the macro BS.
The above-mentioned FBS may be operated in an Out Of Service (OOS) mode (or a service unavailable mode) when a predetermined condition is satisfied. The FBS is unable to provide a normal service during the OOS mode, such that there is needed an effective method that informs an MS of FBS status information before or after the FBS enters the OOS mode.